A distinctive engraving may hold the key to finally solving the mystery of a man found dead in a river on Christmas Day in 1971.
Two teenage girls who went for a swim after lunch found his badly decomposed body at Buxton in the Yarra Ranges, east of Melbourne.
A police probe found no evidence of how he came to be there, how he died or who he was.
It is believed he was in the water for several weeks but after no new leads for 53 years, investigators on Monday issued a fresh appeal for answers and released an image of his unusual signet ring.
It was originally thought to contain an inscription in English, however it may actually be in a different language.
It appeared to read "21.4.71 P.U.C.K" but police believe the letters may spell 'risk' in Cyrillic, an alphabet used in eastern Europe and parts of Asia.
The man was found about 4km downstream from a Ukrainian youth camp and 60m from a major bridge over the Steavenson River.
The engraved numbers could be a wedding date or another important milestone, Victoria Police Detective Sergeant Flyn Loughlin said.
"It's a vital piece of information I think can assist us with identifying who he is," he said.
Investigators have been in touch with the Ukrainian embassy and local youth camp, but neither were able to shed any light on the man's identity.
"This man belongs to someone, someone's missed him, he's someone's son and I'm hoping that someone out there can provide us with that piece of information to solve who he is," Det Sgt Loughlin said.
The unknown man had a large build and was believed to be aged in his 30s to 50s with dark, greying hair.
He wore a white shirt, vest with square white buttons, blue jeans, a belt, desert-style boots and had a gold Unicorn watch.
A second, thick belt was worn around his stomach and detectives believe it may have been used to support his abdominal muscles.
His body was so badly decomposed it was impossible to tell if he was injured before his death, with a coroner determining his cause of death was consistent with drowning.
There were no signs of a fishing accident or a fall and no personal property was found nearby, giving police no reason to believe his death was suspicious.
The discovery attracted significant media attention at the time and he was checked against missing persons records, while a dental record search failed to turn up any clues.
It happened around the same time as the disappearance of unionist Alfred 'The Ferret' Nelson whose car was found at the Yarra River, however physical characteristics ruled out the possibility it was his body.
The unknown man was buried at Springvale cemetery, with hopes one day his name will appear on a headstone.
